JP2009-013753A describes this type of control valve.
Further, a conventional valve shown in FIG. 3 is known as this type of control valve. In the control valve shown in FIG. 3, a spool 2 is incorporated into a valve main body 1 to be free to slide, and a spring force of a centering spring 3 is exerted on the spool 2. Respective ends of the spool 2 oppose pilot chambers 4, 5, and the spool 2 is switched by an action of a pilot pressure led to one of the pilot chambers 4, 5 such that one of a pair of actuator ports 6, 7 formed in the valve main body 1 communicates with a pump and the other communicates with a tank.
A signal pressure passage 8 that transmits the pilot pressure of the pilot chamber 4 or 5 as a signal pressure of another device is formed in the valve main body 1. The signal pressure passage 8 communicates with the pilot chamber 4 via a check valve 9. The check valve 9 allows working oil to flow only from the pilot chamber 4 into the signal pressure passage 8.
The pilot chamber 5 communicates with the signal pressure passage 8 via a connecting hole 10 formed in the spool 2 and a check valve 11 provided in the connecting hole 10. The check valve 11 allows working oil to flow only from the pilot chamber 5 into the signal pressure passage 8.
When the pilot pressure is led into the pilot chamber 4, the spool 2 moves in a rightward direction of the figure against the spring force of the centering spring 3 such that the actuator port 7 communicates with the pump and the actuator port 6 communicates with the tank. At this time, the pilot pressure led into the pilot chamber 4 pushes open the check valve 9 so as to be led into the signal pressure passage 8, and is then led from the signal pressure passage 8 into the other device.
When the pilot pressure is led into the pilot chamber 5, the spool 2 moves in a leftward direction of the figure against the spring force of the centering spring 3 such that the actuator port 6 communicates with the pump and the actuator port 7 communicates with the tank. At this time, the pilot pressure led into the pilot chamber 5 pushes open the check valve 11 via the connecting hole 10 so as to be led into the signal pressure passage 8, and is then led from the signal pressure passage 8 into the other device.
Thus, an actuator operated by the control valve is synchronized with the other device.